In a mobile communication system of CDMA, since a plurality of user signals is transmitted in the same band, a signal that a radio receiving apparatus receives is subjected to interference by various signals to cause deterioration of characteristics.
An array antenna is known as an apparatus for eliminating the interference. The array antenna is composed of a plurality of antenna elements, and is capable of setting reception directivity freely by providing adjustment of each of amplitude and phase to a signal received by each antenna element. In this case, adjustment of amplitude and phase provided to the received signal can be carried out by multiplying the received signal by weighting factor (hereinafter referred to as “reception weight”). The radio receiving apparatus can intensively receive only a signal coming from a desired direction by adjusting the reception weight by which the received signal is multiplied.
Another apparatus for eliminating the interference, an interference canceller is known. The interference canceller is a technique for canceling a signal (interference) transmitted from other communication partners other than current communication partner from the received signal to extract a desired signal from the received signal. Conventionally, as an apparatus for canceling interference signals, there are apparatuses described in 1) “Sequential Channel Estimation Type Serial Canceller Using a pilot Symbol in DS-CDMA (Technical Bulletin, RCS95-50, July 1995, Radio Communication System Research Society of the Institute of Electronics, Information and Communication Engineers)” authored by Sawahashi, Miki, Andoh, and Higuchi, 2) “Sequential Transmission Line Estimation Type CDMA Multistage Interference Canceller Utilizing a Symbol Replica Process (Technical Bulletin, RCS96-171, February, 1997, Radio Communication System Research Society of the Institute of Electronics, Information and Communication Engineers)” authored by Yoshida and Ushirokawa, and 3) “Study of CDMA Interferences Canceller in an Upstream Line(Technical Bulletin, RCS96-121, January, 1997, Radio Communication System Research Society of the Institute of Electronics, Information and Communication Engineers)” written by Uosugi, Katch, and Honma. The above three apparatuses are hereinafter referred to as 1) a serial type interference canceller, 2) a parallel type interference canceller, and 3) a symbol ranking type canceller.
Here, it can be expected that the use of combination of the array antenna and the interference canceller provide a larger interference cancellation effect than each independent use.
However, in the radio communication system that provides reception directivity to each channel corresponding to each communication partner by use of the array antenna, degree of interference with respect to each communication partner is different from one communication partner to another. Accordingly, in the case of applying the interference canceller to such the system, it is necessary to individually provide the interference canceller to each channel corresponding to each communication partner. Hence, the simple combination of the array antenna and the interference canceller increases the amount of calculations and the apparatus scale, making it difficult to implement such an apparatus in consideration given to actual hardware design.